This invention relates to four-cycle engines and, more particularly, to small, operator-carried, four-cycle engines having a crankcase vent for preventing oil loss.
Operator-carried power tools such as line trimmers, blower/vacuums, chain saws and the like are typically powered by two-cycle internal combustion engines or electric motors. Two-cycle engines have well recognized exhaust emission problems. Until relatively recently, it was believed that four-cycle engines were too heavy and could not be operated through the range of orientations necessary for an operator-carried power tool. The present applicant, however, recently introduced a commercially successful four-cycle engine powered line trimmer illustrated in U.S. Pat. Nos. 5,241,932 and 5,421,292 which are incorporated by reference herein.
The Everts ""932 patent describes a number of alternative techniques for lubricating the overhead valves and rocker arms oriented in the valve chamber. A sealed lubricant system is described as a number of alternative mist lubrication systems. The mist lubrication systems enable the engine to be inclined very significantly from the vertical orientation. However, when the engine is run in the inverted position for extended periods of time, oil begins to leak from the engine breather.
It is an object of the present invention to increase the length of time an operator-carried, four-cycle engine can be run in the inverted position before oil begins to leak from the engine breather.
It is a further object of the present invention to provide simple and easy-to-manufacture engine components to block the flow of oil from the crankcase.
These objects and other features and advantages of the present invention will become apparent upon further review of the specification and the drawings.
A first embodiment of the invention comprises an operator-carried power tool and a lightweight, four-cycle, internal combustion engine for driving a rotary-driven implement. The four-cycle engine is mounted on the frame to be carried by the operator in a normal operating position. The four-cycle engine includes a lightweight block defining a cylindrical bore and crankcase, an enclosed cam case and a cam bearing. The engine includes a conventional piston and connecting rod reciprocating within the cylindrical bore in cooperation with a crank pin of the crankshaft.
The crankshaft is provided with an axial shaft rotatably mounted on the engine block. The crankshaft has an internal axial passageway formed therein with two axial, spaced-apart inlet/outlet ports and a crankshaft web-counterweight affixed to the axial shaft and the crank pin. The web-counterweight has an internal radially extending passageway in communication with one of the inlet/outlet ports of the axial shaft. The second inlet/outlet port of the axial shaft is in communication with the cam case to thereby interconnect the cam case and the crankcase via the crankshaft passageway. When the engine is in operation, the rotating passageway precludes the flow of free oil and large oil droplets from the crankcase to the cam case while allowing oil mist laden air to pass freely therebetween.
A second embodiment of the invention comprises a camshaft that has a central opening through which an oil mist generated by a splasher may pass from the crank case to the cam case portion of the engine housing. A port located in the camshaft allows oil droplets to be centrifuged from the central opening in the camshaft to the cam case from which oil is drained back to the crankcase. In this way, liquid oil is separated from the oil mist. The oil mist passes through an oil mist flow passage that extends to the valve chamber at the upper region of the engine assembly.